This invention relates in general to a broadband coupler and in particular, to a broadband coupler employing two or more layers of material where each layer reflects and passes predetermined percentages of power where the percentages are substantially independent of wavelength of the radiation.
Fused Biconical Taper (FBT) technology is widely used to produce a fiber optic coupler. A Technical Note on FBT couplers entitled "Specifying Fiber Optic Couplers" published by Gould Inc., Glen Burine, Md., introduces the FBT technology and its advantage and challenge. FBT technology is an easy and cheap method for making fiber optic couplers. However, the FBT coupler is wavelength dependent. Furthermore, cascading multiple 1.times.2 couplers is required to make a uniform multi-port splitter resulting in large packaging size and extra labor cost.
A 1.times.4 coupler in the product catalog entitled "Single-Mode Fiber Optic Components" of Selco Products Co., Buena Park, Calif., is shown in FIG. 1, where the coupler is composed of three 1.times.2 couplers connected by fibers. To reduce excessive fiber bending, the length and width of the housing need to be of the order of three inches. At such size, the coupler occupies too much valuable space for many applications.
In modern wavelength division multiplexing (WDM) communication, it is often desirable and sometimes required to use wavelength insensitive components for the broad bandwidth operation of the WDM system. The FTB described above is not practical for such applications.
It is therefore desirable to provide an improved wavelength independent multiport coupler for modern WDM communication and other applications.